An X-ray survey of the 2 Jy sample – II. X-ray emission from extended structures

Abstract

The 2Jy sample is a survey of radio galaxies with flux densities above 2 Jy at 2.7 GHz. As part of our ongoing work on the southern subset of 2Jy sources, in paper I of this series we analysed the X-ray cores of the complete 2Jy sample with redshifts 0.05 < z < 0.7. For this work we focus on the X-ray emission associated with the extended structures (jets, lobes, and environments) of the complete subset of 2Jy sources with 0.05 < z < 0.2, that we have observed with Chandra. We find that hotspots and jet knots are ubiquitous in FRII sources, which also inhabit systematically poorer environments than the FRI sources in our sample. Spectral fits of the hotspots with good X-ray statistics invariably show properties consistent with synchrotron emission, and we show that inverse-Compton mechanisms under-predict the X-ray emission we observe by 1-2 orders of magnitude. Inverse-Compton emission is detected from many of the lobes in our sample, and we find that the lobes of the FRII sources show magnetic fields lower by up to an order of magnitude than expected from equipartition extrapolations. This is consistent with previous results, which show that most FRII sources have electron energy densities higher than minimum energy requirements.cores of the 2Jy sources in the subset of Dicken et al. (2008), using data from Chandra and XMM-Newton, and found our results to be in good agreement with those of Hardcastle et al. (2006Hardcastle et al. ( , 2009 on the 3CRR radio galaxies.In this work we focus on the extended X-ray emission (jets, hotspots, and lobes) and the environments of the 0.05 < z < 0.2 subset of sources that we have observed with Chandra, whose nuclei we studied in paper I. Our knowledge of X-ray jets (see e.g. the review by Worrall 2009) and hotspots (e.g. Hardcastle et al. , 2007bMassaro et al. 2010Massaro et al. , 2015 has certainly improved over the last two decades, as has our understanding of the environment in which radio galaxies live (e.g. Belsole et al. 2007;Croston et al. 2008;Ineson et al. 2013Ineson et al. , 2015, but the samples of radio galaxies with available detailed observations are still relatively small, and more work needs to be done to understand their extended structures and how they co-evolve with the hosts (see also the recent review by Tadhunter 2016). The 2Jy sample is important in that it is not only statistically complete, but uniformly observed, with c 0000 The Authors

Hard X-ray-selected giant radio galaxies – I. The X-ray properties and radio connection

“…From Chandra data, Mingo et al (2014) concluded that the Xray spectrum is dominated by an accretion-related continuum, absorbed by a column density of around 1.5 × 10 23 cm −2 . From the same data, Mingo et al (2017) detected synchrotron X-ray emission from one of the hotspots.…”

“…All in all, the X-ray emission is consistent with being accretion-related and possibly due to a hot Comptonizing corona, that could be outflowing. The jet component could give a significant contribution, at least in the soft X-ray band (Hardcastle et al 2006(Hardcastle et al , 2009, but is unlikely to dominate the overall emission in most sources (see also Mingo et al 2017). In the case of PKS 2331-240, the X-ray emission is consistent with originating from external inverse Compton scattering in the jet (Hernández-García et al 2017), but this is the only source of our sample classified as a blazar.…”

The intergalactic magnetic field probed by a giant radio galaxy

“…When calculated in this manner the lobe equipartition field strength is usually found to be overestimated, by a factor of 2 to 3, compared to that found from X-ray Inverse Compton observa-Article number, page 6 of 12 S. P. O'Sullivan et al: The intergalactic magnetic field probed by a giant radio galaxy tions of lobes (e.g. Ineson et al 2017;Mingo et al 2017). This highlights some of the uncertainties in the calculation of equipartition magnetic field strengths in radio galaxies (e.g.…”

Unmasking the history of 3C 293 with LOFAR sub-arcsecond imaging

“…A detailed derivation for the equipartition magnetic field is given in Worrall & Birkinshaw (2006). X-ray emission from the outer lobes is used for a more direct probe for the magnetic field strength, since it is understood to originate from the inverse-Compton scattering between the relativistic electrons and the CMB photons (for example Feigelson et al 1995;Isobe et al 2002;Hardcastle et al 2002;Mingo et al 2017). In the last two decades, studies using IC-CMB X-ray emission have found that for FRII galaxies, magnetic field strengths are lower than the equipartition values by a factor of 2-3 (Croston et al 2005;Ineson et al 2017;Turner et al 2017).…”